In succession to blue ray HD-DVD, the optical disk storage technology is estimated to seek even higher density storage media, such as near field storage, 3D storage technology etc. This causes the distance between the pickup head of a disk drive and a disc to be smaller, thus the pickup head of the disk drive is more sensitive to the vibrating interference of the disc in rotation. Since a disc in rotation generates a significant amount of vibration, so the optical disk drive module in the disk drive adapts the rotational speed of the disc according to the read/write status such that the speed is suitable for data read, write or erase. The -rotational speed of a disk drive is therefore not constant, and the generated main vibrating frequency is not constant either.
Traditional dynamic vibration absorbers applied to disk drives can only absorb vibration for certain frequencies, for example those that have been successfully applied to disk drives by manufacturers such as Lite-ON, ASUS or Pioneer etc. FIG. 1 is a schematic view of a traditional vibration absorber 11 applied to a disk drive. The vibration absorber 11 consists of a plurality of second elastic members 111 and a damper associated with the second elastic member 111. The vibration absorber 11 is integrated to an optical disk drive module 13 of the disk drive 1. The optical disk drive module 13 is disposed on a carrier 14 with a first elastic member 12. The first elastic member 12 is coupled to a housing 15 of the disk drive 1. The first elastic member 12 reduces the vibration produced by the rotation of the optical disk drive module 13, whereas the vibration absorber 11 absorbs the vibration of the optical disk drive module 13.
The theoretical configuration of the vibration absorber 11 disposed on the optical disk drive module 13 of the disk drive 1 is shown in FIG. 2, and the motion equations of the optical disk drive module 13 are represented by:m1{umlaut over (x)}1+c1{dot over (x)}1+c2({dot over (x)}1−{dot over (x)}2)+k1x1+k2(x1−x2)=F(t)=pω2ejωm2{umlaut over (x)}2+c2({dot over (x)}2−{dot over (x)}1)+k2(x2−x1)=0
wherein m1 is the mass of the optical disk drive module 13, m2 is the mass of the damper 112, x1is the vibrating shift of the optical disk drive module 13, x2 is the vibrating shift of the damper 112, F(t) is a function of the rotational unbalance force with respect to time, p is the amount of rotational unbalance, ω is the rotational speed, k1 is the elasticity of the first elastic member 12, k2 is the elasticity of the second elastic member 111, c1 is the damping of the first elastic member 12 and c2 is the damping of the second elastic member 111.
The above motion equations can be simplified such that the vibrating shift x1 of the optical disk drive module 13 can be expressed as:
                X      1            =                                                        {                                                                    [                                                                  k                        2                                            -                                                                        ω                          2                                                ⁢                                                  m                          2                                                                                      ]                                    ⁢                                      Δ                    R                                                  +                                                      c                    2                                    ⁢                                      ωΔ                    I                                                              }                        2                    +                                    {                                                                    c                    2                                    ⁢                                      ωΔ                    R                                                  -                                                      [                                                                  k                        2                                            -                                                                        ω                          2                                                ⁢                                                  m                          2                                                                                      ]                                    ⁢                                      Δ                    I                                                              }                        2                                                Δ          R          2                +                  Δ          I          2                      ⁢    p    ⁢                  ⁢          ω      2      
As can be understood from the above, when the resonance frequency of the vibration absorber 11 equals the frequency of an external force, i.e.,
                              k          2                /                  m          2                      =    ω    ,the vibrating shift of the optical disk drive module 13 is at minimum. However, the elasticity k2 of the second elastic member 111 and the mass m2 of the damper 112 are constant values, thus the absorber only absorbs vibration at a certain frequency (i.e. certain rotational speed). Once the rotational speed of the optical disk drive module 13 changes, the vibration cannot be effectively absorbed, sometimes even greater vibration is caused.
Thus, there is a need for a vibration absorber to suppress the vibration generated at various rotational speeds by the optical disk drive module and solve the shortcomings of the prior art.